Insect pests are a major cause of crop losses. Solely in the U.S., about $7.7 billion are lost every year due to infestation by various genera of insects. In addition to losses in field crops, insect pests are also a burden to vegetable and fruit growers, to producers of ornamental flowers, and they are a nuisance to gardeners and home owners.
Insect pests are mainly controlled by intensive applications of chemical insecticides, which are active through inhibition of insect growth, prevention of insect feeding or reproduction, or death of the insects. Good insect control can thus be reached, but these chemicals can sometimes also affect other, beneficial insects. Another problem resulting from the wide use of chemical pesticides is the appearance of resistant insect varieties. This has been partially alleviated by various resistance management strategies, but there is an increasing need for alternative pest control agents. Biological insect control agents, such as Bacillus thuringiensis strains expressing insecticidal toxins like .delta.-endotoxins, have also been applied with satisfactory results, offering an alternative or a complement to chemical insecticides. Recently, the genes coding for some of these .delta.-endotoxins have been isolated and their expression in heterologous hosts have been shown to provide another tool for the control of economically important insect pests. In particular, the expression of insecticidal toxins in transgenic plants, such as Bacillus thuringiensis .delta.-endotoxins, has provided efficient protection against selected insect pests, and transgenic plants expressing such toxins have been commercialized, allowing farmers to reduce applications of chemical insect control agents. Yet, even in this case, the development of resistance remains a possibility and only a few specific insect pests are controllable. Consequently, there remains a long-felt but unfulfilled need to discover new and effective insect control agents that provide an economic benefit to farmers and that are environmentally acceptable.